Hello from the Pacific tuna taggers!

Photo credit: SPC/Chris Stoehr

By Giulia Anderson
SPC scientist, on board of the Gutsy Lady 4

Napo'opo'o native, Giulia Anderson, is SPC fisheries molecular geneticist embarked on the 2021 6-week research expedition to monitor the health of world’s largest tuna fishery, which is an activity that no other SPC scientist was not able to do this year, for the second time, due to the COVID-19 pandemic.

So much progress has been made since the first days on this vessel, Gutsy Lady 4! The four scientists – Jeff, Ben, Chris and me (Giulia) – are now perfectly integrated into life on this boat with its crew of six: Tim, the captain, and five sailors, all from Indonesia.

Another day, same planet

Getting up every day at 2:00 am to catch tuna near fish aggregating devices (FADs) with rods and reels or hand lines has become a routine that no one questions. The start-up of the two 600-horsepower engines is the best wake-up call ever!

Awake before everyone else and having started the coffee pot, Tim manoeuvres the boat slowly towards the FADs estimated position while the others emerge from their cabins and head to the aft deck to gear up and prepare for battle... Some need to drink their mug of coffee first, others need to eat and there is always one who start the music playlist that will set the pace for the action on deck! For today, it is salsa!

The conventional tags are placed at the head of the scoring tables and Jeff prepares his electronic tags and “surgical equipment”. The flashing light from the FAD satellite buoy is triggered from the dedicated computer on the bridge, just behind Tim’s chair. The weather is calm and the flashing is quickly spotted by one of the sailors who points to show Tim the direction. We get there and everyone is at their posts. Using the boat’s dual controls on the front of the deck, Tim stops the boat near the FAD and the fishing can begin: drop the lure to the depth where the tuna are swimming, hook the fish and reel-it in! It sounds easy but you must be a good fisherman to be able to do that.

What would we do without these FADs? Our fishing technique is not suitable for catching tuna in “free school”, at least not in sufficient numbers, so it’s thanks to our collaboration with the fishing industry and Satlink, the satellite buoy provider, that the tuna can be tagged. Ben, Tim, Jeff and Chris use rods and reels combined with heavy metallic lures (weighing 200–300 grams) to jig under the boat, the sailors use hand lines and large landing nets used to get the fish out of the water.
The tuna are often biting at less than 20 metres below the boat and, so far, the vast majority are juveniles weighing between 3 and 7 kg which are easily and quickly caught without any damage to them (and to the fishermen!).

Tagging tuna: A race against the clock

Tuna tagged - SPC/Chris StoehrBetween 100 and 200 fish are taken out of the water before daybreak. Most leave with a conventional tag on their backs, a few of the larger and more vigorous ones are operated on by Jeff who quickly inserts an archival tag into their abdominal cavity before closing the incision with one or two stitches. The fish is back in the water less than two minutes after its capture. We are crossing our fingers to find this tuna one day and to be able to relate the story: a slice of life of a tuna in the ocean.

Some of the less fortunate ones have suffered irreversible damage during their capture and are quickly euthanised and then put aside by me so I can take valuable biological samples from them (stomach, otoliths, muscle, etc.), which will be kept frozen in the boat’s hold and then analysed later in the laboratory. Data on the diet, growth and genome of the tuna is collected this way.

Tuna science in action

Tuna sampling - SPC/Chris Stoehr

These genetic analyses may allow the identification of different populations or “stocks” and thus refine their management. When taking muscle samples for genetic analysis, it is important to ensure that there is no contamination of the sample and no damage before the analysis. This is not easy on a boat that sees thousands of fishes of different species caught in different places. I, therefore, spend a lot of time developing sampling protocols and testing different methods to ensure the integrity of the samples – i.e. no contamination from previous fish that may have passed across the deck. For example, one of my studies aims to estimate the possible degradation of the fish flesh kept in ice, which meant I needed to take samples every two days from the same tuna stored in the hold of the boat. It can be a shock to go from 30 degrees centigrade or more on the deck to zero degrees in the hold!

Here we are at latitude 4° 47' N and longitude 158° 27' W. It has been two weeks since we left Honolulu and already more than 3600 tuna have been tagged, including the placement of 75 archival tags and 138 fish sampled. Not bad, we think; some of us are starting to dream of another tagging record!

Week 3 in the middle of the world’s largest ocean

The weather has been exceptionally calm this week; the ocean is smooth this morning. This also means that the mid-morning fishing sessions are torrid. Oh yes, I forgot to mention that we have changed our tactics: now we don't fish at night because we suspect that it may disturb the school and decrease the efficiency of the daybreak trolling session. It seems to work but the eternal question of why and when the fish will bite still comes to the same conclusion: whenever they want!

Some of the wildest tagging periods were in the middle of the day with fish biting relentlessly for two or three hours at less than 30 metres below the boat. It is unbelievable, but this has happened several times. This led to fishing competitions between the scientists, with the fish leaving with an archival tag worth twice as many points as the others. Even the crew got in on the act. It’s been great for morale! There is no time to make food, but one needs energy for this kind of work under the blazing sun so cold drinks kept in a cooler nearby and a few packets of chips or other snacks allow us to hold on until the fish call an end to this game by going back to the depths.

Fortunately, I can see the end of the degradation experiments on the 40 fish kept in the ice for 10 days. It’s not easy to have to do these samples with your feet in the ice after having fished, tagged and collected samples for five hours in the sun.

We are at 3° 20' N and 166° 34' W and the total fishes tagged now amounts to 4644 conventional tags and 141 archives.

Until the next time …

Blog Category
Blog Post
Fisheries, Aquaculture & Marine Ecosystems


Giulia Anderson

Fish Molecular Geneticist, Fisheries, Aquaculture and Marine Ecosystems Division, SPC